1. Field of the Invention
The invention relates to the manufacture of golf club shafts and more specifically concerns a new process for the manufacture of shafts from composite materials and a device for implementation of this process, as well as the shaft thus manufactured.
2. Description of Background and Relevant Information
A process for the manufacture of tubular objects such as fishing rods and golf clubs made of resin reinforced with carbon or other fibers is described in British Patent No. 1,446,444 and U.S. Pat. No. 4,555,113.
The process involves winding, around a mandrel, sheets or layers of fibers pre-impregnated with epoxy resin, for example, then compressing this stack by taping using a thermoretractable polyester film. The mandrel covered in this way is then placed in an oven in order both to bake the composite covering and to cause compression of the covering around the mandrel through pressure exerted by the retraction of the film. Finally, after hardening of the resin, the mandrel and the tape are removed. Surface irregularities or traces left by the tape, commonly called steps, are abraded by grinding with emery during the shaft-finishing operation.
A variant of this procedure involves dressing the mandrel by filament winding using a yarn preliminarily impregnated with resin.
However, golfers, and especially top-level players, do not find these processes, which are very commonly used by manufacturers, entirely satisfactory, since they do not allow the mechanical properties to be reproduced from one shaft to another.
The substantial differences in the performances of these clubs, which are brought to light by professional golfers, result, in particular, from the removal of material during the required shaft-finishing operation.
Furthermore, these procedures appreciably restrict the opportunities for producing shafts having a complex shape, such as biconical shafts which may or may not incorporate reversed conicity of the areas of enlargement or narrowing, for example.
U.S. Pat. No. 3,755,037 discloses the manufacture of fiber-reinforced tennis or squash racquets and other curved articles. The composite structure of the racquet base is obtained from a tubular member which has a uniform section over its entire length and which is formed in a mold to provide an open oval or loop and spaced apart, parallel handle portions. The process uses an expansible casing which is impermeable to fluids. Pressures on the order of 50 to 100 psi are brought to bear by the fluid introduced inside the casing for expanding the casing and forcing the helical windings into contact with the walls of the mold.
The manufacture, of such structures having portions with complex shapes is obtained, according to the aforementioned process, by adding reinforcements or additional layers at the desired locations.